The present invention relates to an optical resin and a process for preparing the same, and more particularly to an optical resin including a polymer of a special diester of dicarboxylic acid and a process for preparing such an optical resin.
Organic polymer materials have hitherfore been used as substitutes for inorganic glasses, while taking advantage of their excellent properties such as that they are transparent and of light weight and can be handled safely and easily machined.
Representative examples of organic polymer materials which have been used as organic glasses are polymethyl methacrylate, polycyclohexyl methacrylate, polydiethyleneglycol bisallyl carbonate, polycarbonate and polystyrene.
These organic polymer materials are used for wide optical applications while taking advantage of the aforementioned merits, although they are inferior in resistance to scratching or abrasion, refractive indices and resistance to heating. However, since the refractive indices of polymethyl methacrylate, polycyclohexyl methacrylate and polydiethylene glycolbisallyl carbonate are as low as n.sub.D =1.49 to 1.51, it is inevitable that a lens made of any of these materials becomes considerably thicker than that of a lens made of an inorganic glass. Moreover, relatively skillful technology is necessitated to produce a lens by the cast molding method, since the percent shrinkages at the step of heating to cure these materials are extremely high, ranging from 10 to 25%. Furthermore, these materials are inferior in resistance to heating and in resistance to scratching and abrasion.
Although polystyrene and polycarbonate have high refractive indices of n.sub.D =1.59, they are inferior in weather-proof property and detrimental in resistance to chemicals and heating. Another disadvantage of these materials is that they are not adapted for cast molding which is a favorite molding process for the production of articles having various shapes and dimensions. They are generally molded by means of melt molding processes, such as injection molding, by which an optically uniform article is difficult to produce to double refraction resulting from the melt molding.